Oxo-vanadium as a spin probe for the investigation of the metal coordination environment of imidazole glycerol phosphate dehydratase

Imidazole glycerol phosphate dehydratase (IGPD) catalyses the dehydration o f imidazole glycerol phosphate to imidazole acetol phosphate, an important late step in the biosynthesis of histidine. IGPD, isolated as a low molecul ar weight and inactive ape-form, assembles with specific divalent metal cat ions to form a catalytically active high molecular weight metalloenzyme. Ox o-vanadium ions also assemble the protein into, apparently, the same high m olecular weight form but, uniquely, yield a protein without catalytic activ ity. The VO2+ derivative of IGPD has been investigated by electron paramagn etic resonance (EPR), electron nuclear double resonance (ENDOR) and electro n spin echo envelope modulation (ESEEM) spectroscopy. The spin Hamiltonian parameters indicate the presence of multiple N-14 nuclei in the inner coord ination sphere of VO2+ which is corroborated by ENDOR and ESEEM spectra sho wing resonances attributable to interactions with N-14 nuclei. The isotropi c superhyperfine coupling component of about 7 MHz determined by ENDOR is c onsistent with a nitrogen of coordinated histidine imidazole(s). The ESEEM fourier-transform spectra further support the notion that the VO2+ substitu ted enzyme contains inner-sphere nitrogen ligands. The isotropic and anisot ropic N-14 superhyperfine coupling components are similar to those reported for other equatorially coordinated enzymatic histidine imidazole systems. ESEEM resonances from axial N-14 ligands are discussed. (C) 2000 Elsevier S cience Inc. All rights reserved.